Traditional multi-band low-profile parabolic antennas bear the disadvantages of complex structure and the inability to multi-band work simultaneously. A novel design method is introduced in this paper. The proposed quad-band antenna works on the frequency of 14-14.5 GHz, 11.45-12.75 GHz, 19.6- 21.2 GHz, 29.4-31 GHz. The whole antenna adopts a two-slot-depths horn feed, shaped sub-reflector and main reflector. The reflectors are designed by the aperture field distribution function and polynomial transition function. The overall antenna structure is optimized with full-wave electromagnetic software. The test result shows the efficiency in the entire frequency band is improved by at least 12%, and the first side lobe is controlled below -14 dB, which meets the performance requirements. This design has been applied to actual equipment successfully.